229 



PROCEEDINGS. 



January 12th, 1883. — Conversational Meeting. 



A demonstration on " Photomicrography' was given by Mr. T. Charters 

 White, F.L.S., F.R.M.S., in one of the class rooms, to a large gathering of 

 members. 



As the various processes had necessarily to be carried out in a darkened 

 room, Mr. White, before entering on the modus operandi, explained shortly 

 the simple apparatus he had devised and used with some success, for obtain- 

 ing enlarged photographs of microscopic objects, which, though not fine 

 examples of photography, were useful to illustrate and explain objects ex- 

 hibited under the microscope. Such a photograph placed by his microscope 

 with a few descriptive remarks and reference letters on the photograph, 

 enabled him to direct attention to any points of interest in the specimens 

 exhibited, and it was not necessary to stand by the microscope a whole even- 

 ing to explain the object he was showing. 



The method most generally practised and recommended was that the 

 microscope being placed in a horizontal position, its tube should be attached 

 by a blackened tube or cone to the front of a photographic camera, the lens 

 of which had been removed. Then these difficulties arose. It was not 

 everyone who had a camera, and they might not feel disposed to go to the 

 expense of procuring one, while all the members of the Club possessed 

 microscopical objectives ; but, further, if they had a camera, it was not an 

 easy matter to see the fine details of a subject through the ordinary ground 

 focussing glass. Again, unless the camera and microscope were securely 

 fastened down to a base-board, there was a tendency to unsteadiness, which 

 was irritating in the extreme ; and further, the usual plan did not offer any 

 advantages over that he wished to introduce to the notice of the members. 



In the apparatus on the table, and which had been found so convenient, it 

 was not necessary to have either a camera or a microscope, and it was so simple 

 that it could be adopted by the youngest member of the Club ; but even with 

 that, difficulties would arise which were altogether apart from the apparatus. 

 For instance, objects differed in their capability of transmitting the actinic 

 rays ; they might be too opaque or brown, or they might be stained blue or 

 red. All these conditions varied the time of exposure, only experience teach- 

 ing the requisite time to imprint the image on the sensitive film just suffi- 

 ciently without under or over exposure : that must be left to the cultivated, 

 judgment of the operator. Great assistance would be derived by the beginner 

 keeping to one objective until he could produce a good result on every occa- 

 sion, when a fresh one might be tried, the time of exposure being greatly 

 varied by the magnifying power employed, the lower powers admitting of a 

 shorter exposure, as more light passed through them. 



Journ. Q. M. C, Series II., No. 5. s 



